It should be on your computer. How did you get it to the ipod in the first place?
The music sync is one way - computer to ipod. The exception is itunes purchases. Without syncing: File>Transfer Purchases
The ipod touch is not a storage device. It is designed to mirror the elected content from your computer.
What's more,you can refer this article about how to transfer or copy music from iPod to computer, which included an easy guide to work out that.
Cheers.